1. Field of the Invention
The present invention generally relates to a method of designing a connecting rod for an internal combustion engine. More specifically, the present invention relates to a design method that helps reduce the weight of a connecting rod for an internal combustion engine.
2. Background Information
An internal combustion engine has a connecting rod that interconnects a crank shaft to a piston such that rotational movement of the crank shaft is translated to reciprocal movement of the piston. Examples of connecting rods are disclosed in Japanese Laid-Open Utility Model Publication No. 5-45222 and Japanese Laid-Open Patent Publication No. 5-202923. These publications disclose methods of producing lightweight, high-strength connecting rods for internal combustion engines.
In particular, Japanese Laid-Open Utility Model Publication No. 5-45222 discloses an internal combustion engine connecting rod structure that includes a connecting rod main body, a cap and a pair of bolts serving to fasten the connecting rod main body and the cap together. The connecting rod main body has a piston pin hole formed in one end and half of a crank pin hole formed in the other end. The cap is arranged on the other end of the connecting rod main body such that the crank pin hole lies between the connecting rod main body and the cap. A bolt bearing surface is formed on the connecting rod main body. An undercut section is formed at the boundary portion between the bearing surface and a perimeter wall that intersects with the bearing surface. The undercut section is shot peened to impart a compressive residual stress in the boundary portion.
On the other hand, Japanese Laid-Open Patent Publication No. 5-202923 discloses a connecting rod comprising a connecting rod main body, a first large end half body that has internally threaded holes and is provided integrally on one end of the connecting rod main body, and a second large end half body that is fastened to the first large end half body with two bolts. The connecting rod main body and the second large end half body are made of a sintered aluminum alloy. The connecting rod is designed such that the fracture toughness of the first large end half body is larger than the fracture toughness of the second large end half body and the Young's modulus of the second large end half body is larger than the Young's modulus of the first large end half body. According to the publication, this design improves the fatigue fracture strength at the bottom of the valleys of the internal threads.
In both cases disclosed in the above mentioned publications, in order to design the bolts used for fastening the cap to the connecting rod main body, it is necessary to analyze the strength of the bolts in a standalone fashion.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved method of designing a connecting rod for an internal combustion engine. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.